Blood Spatter Analysis Lecture - part 1
Summary
TLDRThis lecture delves into the intricate field of blood spatter analysis, a crucial forensic technique. It covers how blood patterns reveal information about the crime, such as weapon type, number of blows, and victim position. The talk introduces various detection methods, including light sources, presumptive tests, and reagents like luminol and phenalene. It also explores the significance of blood spatter patterns, the physics of blood drop formation, and the use of trigonometry to determine angles of impact, ultimately helping to identify the crime's point of origin.
Takeaways
- 🔎 Blood Spatter Analysis (BSPA) examines patterns of blood stains to determine various aspects of a crime scene.
- 🚔 Forensic scientists can deduce information such as the type of weapon used, the speed of the weapon, the number of blows, and the position of the assailant and victim.
- 🕵️♂️ Different techniques are used to detect blood, including specific light sources and filters, presumptive tests, and reagents like phenalene and heem sticks.
- 💡 Luminol is a chemical that reacts with blood to create a blue glow, useful for revealing blood stains that are not visible to the naked eye.
- 🚫 Bleach can interfere with the detection process, as it reacts with certain chemicals used for blood detection, leaving a smudge instead of a glow.
- 💚 Florene is another chemical that can be used for detecting fine blood stains, causing them to glow greenish-white.
- 📸 Crystal Violet is used for creating a purple color in blood stains for photographic documentation, helping to identify shoe types and footprints.
- 🔍 Blood stain patterns are categorized by the force applied, such as low, medium, or high velocity spatters, and can indicate the direction of the blood flow.
- 📏 The size and shape of blood drops can provide information about the distance and angle of the blood drop, influenced by factors like the volume and the surface it falls on.
- 📐 Trigonometry is used to calculate the angle of impact from blood drops, with measurements of width and length plugged into a spreadsheet for precise calculations.
- 📍 The point of origin and area of origin can be determined by analyzing the pattern and direction of blood spatters, converging to the point where the incident occurred.
Q & A
What is the main focus of the lecture?
-The lecture focuses on blood spatter, discussing the patterns that blood stains present on different surfaces and the techniques forensic scientists use to detect and analyze them.
What does BSPA stand for in the context of the lecture?
-BSPA stands for Blood Stain Pattern Analysis, which is a method used by investigators to analyze the patterns of blood spatter at crime scenes.
What can forensic scientists deduce from blood spatter analysis?
-Forensic scientists can deduce the type of weapon used, the speed of the weapon, the number of blows, the handedness of the assailant, the position of the victim, the sequence of wounds, the movement of the assailant, and the time of death from blood spatter analysis.
What are the different light sources that forensic scientists might use to detect blood?
-Forensic scientists may use different light sources such as a flashlight with a particular filter or UV lights to make blood stains visible that are not visible to the naked eye.
What is a presumptive test in the context of blood detection?
-A presumptive test is a chemical test that reacts with the properties of hemoglobin to indicate the presence of blood, but it does not confirm if the blood is human.
What is the purpose of using phenalene or a heem stick in blood detection?
-Phenalene or a heem stick are reagents used to swab a surface; if blood is present, the swab turns pink, indicating the presence of blood.
What is the chemical luminol used for in blood detection?
-Luminol is a chemical used in blood detection that glows blue when sprayed on a surface, revealing blood stains that are not visible under normal lighting conditions.
What is the difference between a transfer and a contact blood stain pattern?
-A transfer blood stain pattern occurs when blood is wiped or smeared onto a surface, while a contact pattern is created by direct contact between the blood source and the surface.
What is stringing and how is it used in blood spatter analysis?
-Stringing is a technique used in blood spatter analysis where a string is run through elliptical blood drops to determine the direction of the blood flow and to help identify the origin of the blood spatter.
How do forensic scientists determine the angle of impact from a blood drop?
-Forensic scientists use trigonometry to measure the width and length of a blood drop, calculate the sine of the angle, and determine the angle of impact.
What is the significance of the point of convergence in blood spatter analysis?
-The point of convergence is where lines drawn through the elliptical blood drops intersect, indicating the area or point of origin of the blood spatter, which helps in understanding the crime scene dynamics.
How does the height of a blood drop affect its size and the resulting spatter pattern?
-The height from which a blood drop falls affects its speed and, consequently, its size and the diameter of the resulting spatter pattern. The higher the drop, the larger the diameter, until it reaches a maximum due to air resistance.
What factors influence the shape of a blood drop when it hits a surface?
-The shape of a blood drop when it hits a surface is influenced by the volume of the drop, the speed at which it falls, and the type of surface it lands on, such as smooth glass or rough cardboard.
What is the significance of spines in blood drop analysis?
-Spines are elongated extensions from the main drop that can indicate the height from which the drop fell and the type of surface it landed on, providing clues about the crime scene.
How do forensic scientists use the shape of blood drops to determine the direction of flow?
-Forensic scientists look at the shape of blood drops, particularly the elongated droplets, to determine the direction of flow. The tail of the droplet points in the direction the blood was traveling when it fell.
Outlines
🔎 Introduction to Blood Spatter Analysis
The lecture introduces the concept of blood spatter analysis, a forensic science technique used to interpret patterns of blood stains on various surfaces. The abbreviation 'BSPA' stands for Blood Stain Pattern Analysis, which helps investigators deduce information such as the type of weapon used, the speed and number of blows, the position of the victim, and the sequence of events at a crime scene. The lecture also mentions the use of different light sources and presumptive tests to detect blood, including UV lights and reagents like phenalene, as well as the use of luminol to reveal blood presence through a blue glow. Additionally, the importance of understanding blood spatter patterns for determining the crime scene's location and the use of stringing or lasers to analyze the spatter's distribution are discussed.
📚 Understanding Blood Spatter Patterns and Techniques
This paragraph delves deeper into the types of blood spatter, including round and elongated drops, and the significance of these patterns in determining the direction of blood flow and the origin of the stains. The concept of 'spines' radiating from a parent drop and 'satellites' as smaller drops that break away are explained. The impact of factors like drop height, volume, and surface type on the formation of these patterns is discussed. The paragraph also covers the use of basic physics and trigonometry to calculate the angle of impact and the point of origin of the blood spatter. The importance of precise measurements in millimeters for accurate analysis is emphasized, and the process of using stringing or laser technology to find the area and point of origin at a crime scene is described.
📉 Advanced Blood Spatter Analysis: Point of Origin and Convergence
The final paragraph focuses on advanced techniques in blood spatter analysis, specifically the determination of the point of origin and point of convergence. It explains how CSIs use elliptical blood drops to draw lines that intersect at the area of origin, and how the point of convergence indicates the source of the blood spatter. The paragraph introduces the concept of using three-dimensional analysis, including height (Z-axis), to accurately pinpoint the origin. It also discusses the use of Excel spreadsheets with pre-populated formulas to assist with trigonometric calculations for determining angles of impact based on the width and length of blood drops. The importance of accurate measurements and the process of stringing to visualize the intersection points for origin determination are reiterated.
Mindmap
Keywords
💡Blood Spatter
💡BSPA
💡Forensic Scientists
💡Presumptive Test
💡Luminol
💡Florene
💡Crystal Violet
💡High-Velocity Spatters
💡Transfer
💡Stringing
💡Satellites
💡Trigonometry
Highlights
Blood spatter analysis (BSPA) is used to determine patterns of blood stains on various surfaces.
Forensic scientists can deduce information such as the type of weapon used, weapon speed, number of blows, victim position, and handedness from blood spatter patterns.
Investigators can discern the sequence of wounds and the movement of the assailant around the victim through blood spatter.
Different drying times and immediate or delayed death can be inferred from the blood spatter at a crime scene.
Forensic tools such as specific light sources and filters can reveal blood stains not visible to the naked eye.
Presumptive tests react with hemoglobin properties but cannot confirm human blood without lab analysis.
Swabbing and reagent application, such as phenalene or a heem stick, can confirm the presence of blood with a color change.
Luminol is a chemical that reacts with blood to produce a blue glow, useful for detecting cleaned-up crime scenes.
Chemical reactions with substances like bleach can interfere with blood detection methods.
Florene is used for fine stains and smears, producing a greenish-white glow, but can also react with non-blood substances.
Crystal Violet is applied for photographic imaging of blood patterns, resulting in a purple coloration.
Different types of blood spatter patterns indicate the force and method of the crime, such as passive drops, projected stains, and transfer/contact stains.
Stringing or laser technology helps determine the crime scene by analyzing the positioning of blood spatter.
Elongated blood drops can indicate the direction of blood flow and the origin of the spatter.
Spines and satellite drops provide additional information about the height and force of the blood drop impact.
Basic physics principles, such as the relationship between drop speed and diameter, are applied in blood spatter analysis.
The volume and surface type affect the appearance of blood drops, influencing the analysis of spatter patterns.
Trigonometry is used to calculate the angle of impact from the dimensions of blood drops.
Excel programs can automate the trigonometric calculations for blood spatter analysis.
The point of origin and point of convergence are critical in determining the location and source of the crime.
Transcripts
welcome for this lecture we're going to
talk about blood spatter and we'll be
looking at different techniques uh what
forensic scientists use to detect blood
and some of this we'll actually do in
our Labs so go ahead and get out your
lecture notes your
spiral okay um when we talk about blood
spatter it is looking at the patterns
that blood stains will present itself on
different types of surfaces so you'll
see the abbreviation
bspa and different forms of that uh but
that stands for blood stain pattern
analysis so what an investigator will
learn from the analysis of different
blood spatter and you may even see it
splatter um but we're going to call it
spatter um the type of weapon that was
used how fast that weapon was moving the
number of blows on a victim
whether the vi the asant was right or
left-handed how he was position he or
she was positioned over the victim um
they can also tell which wounds happened
first um how the as salent would move
around the victim type of injuries they
can even look on how long it was going
depending on how it dried in on the
surface and whether the death was
immediate or
delayed so forensic scientist at a crime
scene CSI will use different types of
sources to detect if the evidence you
may have seen this on different TV shows
so they could use a different light
source um something as simple as a
flashlight with a particular filter on
it um so it may not be visible to the
naked eye but the uh particular filter
and UV lights can detect that they may
also use something called presumptive
test and these would react with
different properties of hemoglobin and
there's different types but it does not
detect if it's human or not so they
would have to take that back to the lab
to determine that but if blood is
present then youve probably seen this
where on different shows they will swab
something and then apply a different
type of reagent uh phenalene is an
example of that um or a heem stick and
if it turns pink then and they always
make that a big drama then blood is
present I know you've heard of this this
is called luminol and it will glow blue
and this is an example so they just by
spraying this of course it has to be
pitch black um or the lights dimmed we
can see here on the couch that there was
a blue stain and then the body was drug
across the room now one of the bad
things they if it has been cleaned up
especially with bleach it will react so
we can see here since it's entire smudge
this particular area was cleaned with a
chemical
um another type of chemical that they
can apply these are for fine stains
smears and this will glow a greenish
white and this is
florene um so it works similar to
luminol but again it can react with
other things like copper and
bleach there is a another um Crystal
Violet lco Crystal Violet and they will
use this if they need a photog graph an
image so as we progress we can see
different Footprints and by the time
they apply it'll be a purple color
violet um they can actually see the type
or make of the shoe by the time they
finish processing it now there are
different types of patterns depending on
the weapon and the method so anything
that's passive this is due to gravity so
these are drops off of a weapon any kind
of flow pattern from a wound or anything
that pulls
a projected blood stain there would be a
a particular Force applied and they will
say that that's low medium or High
Velocity spatters depending on um the
force that's uh placed behind it then
you can also have a transfer or a
contact so this would be if a weapon or
if someone walks through if it's wiped
then it would be categorized as this
okay if it's a blood spattered
but to fall into this definition sorry
um it's just a random distribution of
the stains and it can vary in shape and
size and fenic scientists will use this
to determine where the crime took place
um and we'll do something like this in
class in our lab and and they refer to
it as stringing now we're going to use a
stringing but nowadays they will use
lasers um it kind of speeds up the
process of um processing the crime scene
so they can tell how much blood the
force just by the positioning of the
blood
spatter so we can see here these are
different types of spatters uh we have a
round and these are little satellites
we'll talk about that in a second and
more elongated and they use these
elongated uh spots or blood drops to
determine the direction of the
flow so the origin or source is where it
came from where it originated from so an
example would be like a bad if that was
used as a weapon the angle and this is
where they would use the elongated
drops now I mentioned something about
spines um kind of how it radiates out so
this would be the parent drop and it
would then form spines going out the
higher the drop gets the more spines
there are so if it's real close to the
ground then it would be more uniform
another thing that would cause or not
cause the spines would be the type of
surface that it falls on then anything
that drops away from the parent is
called a satellite so these are small
drops that would break away and hit
another surface and then I already
mentioned the spines that would help
radiate and this would indicate if it's
a large drop and the spines are
projected away from that parent drop
then it's up higher um is where it fell
from okay so when you determine the
distance uh some basic physics come into
play the faster the drop the larger D
diameter so height would play a factor
in that now anytime you get above 7t
that's kind of where the speed will max
out and it's due to air resistance now
we're not going to do any calculations
with that but that's just something to
keep in mind now the drop of the blood
how large it is depends on the volume so
for example if it falls from a needle
something very small obviously the
volume is not going to be as great as if
it comes from a a b
even though it would fall from a greater
distance so those are two factors you
need to keep into mind when you're
looking at drops another thing you need
to look at is the type of surface so
here um a nice clean line around the
perimeter there's not many spines going
off like it is here so if it's a very
smooth surface like glass then it won't
have the spines going off if it falls on
wood or even some kind of a rough
surface like cardboard then you can
notice the spines direct out now
carpet's a little tricky because of the
pile that it would actually absorb the
spot even though it would be the same
volume as these three images at
top okay we talked about or I mentioned
about the direction they can tell from
the angle so what they will do and we'll
help we will use this when we're
stringing or if we had the technology we
would have lasers but it always points
to the direction that it was track
traveling so I like this little saying
here that the tail tells the tail and
when they're referring to the tail they
are talking about the direction or these
droplets that are elongated now if it's
dropped straight down like for example
if someone's walking rather slow and
they have a weapon in their hand and
it's dropping off that's a 90° straight
to the ground um when we start seeing
the elliptical so make sure you know
it's either round or elliptical
that would be on the degrees and I have
a really good visual coming up here in
just a second on one weapon one point of
origin and how the spatter can change on
how that weapon is swung through the
room now we'll do something A variation
of this we're not going to do any math
um mathematical equations that's what
computers are for but I did want to
introduce this to you they do use trig
to determine um the angle of the impact
so they can take a blood drop and they
can measure the width and the length and
find the sign and then the arc sign they
can then determine the angle or the
percent so we have a program in Excel
and it will do the calculations so the
formula is already plugged in so when
we're talking about the width and length
so you need to know this in order to do
the measurements to plug it into the
spreadsheet so the width is always the
narrow part and the length is the
longest part of the drop so it's very
easy to tell here but you would need to
measure in millimeters and be very
precise when determining the width and
the length because that will affect the
mathematical calculation so be aware of
that so we're going to plug this into
like I said the spreadsheet and if it
follows a curve so if I look at my graph
here I can see that on the Y AIS I have
the width and length
ratio and then along the bottom I have
the degrees so as the degrees if I am
about
22° and the ratio is
0.4 um and as I move up on the impact so
as I become more of a rounded rather as
an
elliptical shape then I can see it would
follow this path it would have a
particular Trend anything that diverges
off of that I would go back and take a
look at my measurements as usually where
that takes place okay I kind of thrown
out a point of origin area of origin so
I can can look at the crime scene or
actually CSI would look at a crime scene
and these are the elliptical blood trops
and they would draw a line through it
and string that's where stringing comes
from or a laser and where they intersect
would be the area of
origin okay so where it
converges um is very similar to the area
of origin but the point of converion
will dictate The Source okay so you
would have possibly
different areas of blood splatter maybe
on one wall ceiling two different walls
so they would take the point or the
origin the area of origin and then they
would look at both areas on either wall
and then they can bring it back to the
point of convergence so in the lab it's
going to be referring to three different
points um and so you would look at all
the different blood spatters
now this is just a two-dimensional and
so the Y AIS and the x-axis and where
those lines meet or intersect is the
point of convergence down here and we're
also going to factor in Z how high off
the ground the height of the
drops okay so i' mentioned stringing so
this is an example down here so they've
taken the drops run the string or the
line through the
elliptical um and then where they all
intersect on all these different drops
on the wall would be the point of
origin
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